Aqueous dispersion of cationic polymer

ABSTRACT

An aqueous dispersion of a cationic polymer is disclosed, which is obtained by reacting an ethylene copolymer comprising from 40 to 80% by weight of ethylene and from 20 to 60% by weight of at least one aminoalkyl acrylamide comonomer represented by formula (I): ##STR1## wherein R 1  represents a hydrogen atom or a methyl group; R 2  and R 3  each represents a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms; and n represents an integer of from 2 to 4,  and having a melt index, as measured in accordance with JIS K-6760, of from 10 to 1,000 g/10 min with hydrochloric acid in water to form a quaternary salt and subsequently reacting the resulting quaternary salt with an epihalohydrin compound through addition reaction. The aqueous dispersion provides a coating film having an improved electrical conductivity or produces effects to simultaneously improve degree of sizing and wet strength of paper.

This is a continuation of Ser. No. 119,448, filed Jan. 12, 1987, nowabandoned.

FIELD OF THE INVENTION

This invention relates to an aqueous dispersion of a cationic polymerprepared from a novel ethylene copolymer.

The cationic polymer aqueous dispersion of this invention is useful inthe formation of a soft and water-resistant antistatic orsemi-conductive coating film. Such a coating film can be formed byimpregnating or coating a substrate, such as paper and a plastic film,with the aqueous dispersion and drying.

In an important application, the cationic polymer aqueous dispersion ofthis invention can be applied to an electrographic recording system, inwhich a latent pattern is formed by electrical signals on anelectrographic recording material comprising an electrically insulatingsupport having provided thereon a conductive layer and a recording layerin this order, and a charged toner powder is fixed thereon to obtain avisualized pattern. In this application, the polymer aqueous dispersionaccording to the present invention can be used in the conductive layereither alone or in combination with a metal oxide semi-conductor toprovide an electrographic recording material excellent in filmproperties and recording performance.

In another application, the cationic polymer aqueous dispersion of thisinvention is useful as an additive in paper manufacturing. In somedetail, the aqueous dispersion of the present invention can be added ina process of sheet forming under a neutral or alkaline condition toincrease both degree of sizing and wet strength and is, therefore,suitable for use in the production of paper containers, water-resistantreinforced corrugated boards, and the like. In addition, the cationicpolymer aqueous dispersion of the present invention is promising forapplication to dust-proof paper, packaging paper for IC parts, etc.taking advantage of its effects in reducing surface resistivity orvolume resistivity; heat-sealing paper, etc. taking advantage of itsheat sealability; and colored substrates for laminated decorative platesand colored paper, etc. taking advantage of its properties to fix dyesor pigments.

BACKGROUND OF THE INVENTION

There have been proposed several polymer aqueous dispersions asconductivity-imparting agents or antistatics with which an electricallyinsulating substrate, such as paper and plastic films, is impregnated orcoated, followed by drying. Among them, well known is an aqueousdispersion of a cationic styrene polymer obtained by reactingchloromethylated polystyrene with a tertiary amine to form a quaternarysalt, as disclosed, e.g., in Japanese Patent Publication Nos. 7871/73and 34150/74. However, since a coating film formed by coating thecationic styrene polymer on paper or a plastic film and drying lackssoftness, the substrate tends to curl or the coating film tends tosuffer cracking during preservation, causing adverse influences onsurface conductivity.

In cases where a cationic polymer is used in a conductive layer of anelectrographic recording material, it is generally mixed with a metaloxide semi-conductor, etc. for the purpose of improving conductivity andreducing humidity dependence of surface resistivity as taught, e.g., inJapanese Patent Application (OPI) Nos. 9524/80 and 33133/80 (the term"OPI" as used herein means "unexamined published Japanese patentapplication"). In this connection, the cationic styrene polymer, whenused alone, is insufficient in terms of receptivity to inorganicfillers. The receptivity to the metal oxide semi-conductor is ofparticular importance taking stability of a recorded image in a lowhumidity atmosphere into consideration.

On the other hand, well-known aqueous dispersions of a cationic polymerprepared from an ethylene copolymer include an aqueous dispersionobtained by reacting an ethylene/aminoalkyl acrylate compound copolymerwith an acid in water as disclosed in Japanese Patent Application (OPI)No. 16542/72. This aqueous dispersion is excellent in receptivity toinorganic fillers, such as metal oxide semi-conductors (e.g., zincoxide, tin oxide, titanium oxide, etc.) and, when coated on a substrate,e.g., paper and plastic films, and dried, provides a semi-conductivecoating film having not only softness but resistance to water orsolvents. In spite of these advantages, however, the coating film formedby the aqueous dispersion prepared from an ethylene/aminoalkyl acrylatecompound copolymer has a relatively higher surface resistivity ascompared with that of the cationic styrene polymer Such an aqueousdispersion applied to a conductive layer of an electrographic recordingmaterial fails to attain sufficient recording performance and,therefore, has not yet been put in practical use.

In the field of sheet forming, the system disclosed in Japanese PatentApplication (OPI) Nos. 98304/83 and 180697/83 is noteworthy. Accordingto this system, sizing and wet strength enhancement can be achievedsimultaneously by adding to an aqueous pulp slurry an aqueous dispersionobtained by reacting an ethylene/ aminoalkyl acrylate compound copolymerwith a variety of organic or inorganic acids in water to form aquaternary salt and then reacting it with an epihalohydrin throughaddition reaction.

The inventors have conducted studies toward practical application of theabove-described technique. However, since the aqueous dispersionprepared from the ethylene/aminoalkyl acrylate compound copolymer shouldbe added in a relatively large amount in order to produce effects asexpected, the results obtained were unsatisfactory for practical usefrom the standpoint of economy as compared with the commonly employedsystem wherein a sizing agent and a wet strength agent are used incombination.

Hence, it has been demanded to solve various problems associated withthe conventional aqueous dispersion prepared from an ethylene/aminoalkylacrylate compound copolymer, i.e., insufficient conductivity of acoating film obtained therefrom, and insufficient performance tosimultaneously impart sizing properties and wet strength in sheetforming.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide an aqueousdispersion of a cationic polymer prepared from an ethylene copolymerwhich is practically useful in view of both performance and economy as aconductive layer of an electrographic recording material or an additivefor paper manufacturing.

As a result of extensive investigations, it has now been found that anaqueous dispersion of a cationic polymer prepared from a novel copolymerof ethylene and an aminoalkyl acrylamide comonomer exhibits markedlyimproved conductive film-forming properties as well as markedly improvedeffects to simultaneously impart sizing properties and wet strength ascompared with the conventional cationic polymer aqueous dispersion. Thepresent invention has been completed based on this finding.

In a first embodiment of the present invention, there is provided anaqueous dispersion of a cationic polymer obtained by reacting anethylene copolymer comprising from 40 to 80% by weight of ethylene andfrom 20 to 60% by weight of at least one aminoalkyl acrylamide comonomerrepresented by formula (I) shown below and having a melt index (measuredin accordance with JIS K-6760) of from 10 to 1,000 g/10 min withhydrochloric acid in water to form a quaternary salt and subsequentlyreacting the resulting quaternary salt with an epihalohydrin compoundthrough addition reaction:

Formula (I) is represented by ##STR2## wherein R₁ represents a hydrogenatom or a methyl group; R₂ and R₃ each represents a hydrogen atom or analkyl group having from 1 to 4 carbon atoms; and n represents an integerof from 2 to 4.

In a second embodiment of the present invention, there is provided anaqueous dispersion of a cationic polymer obtained by adding analkylolamine compound to the above-described cationic polymer aqueousdispersion, followed by heat treatment.

Firstly, the aqueous dispersion according to the present invention ischaracterized not only by excellent receptivity to inorganic fillers,such as metal oxide semi-conductors, but by softness of a coating filmformed therefrom which eliminates causes of troubles, such as crackingof a coating film or curling of a substrate, and by satisfactory waterresistance and solvent resistance of a coating film formed therefromwhich leads to higher reliability on practical use as compared withcommercially available aqueous dispersions of cationic styrene polymers.Moreover, the aqueous dispersion of the first embodiment provides asuperior coating film whose surface resistivity is far lower than thatof the coating film obtained by the conventional cationic polymeraqueous dispersion prepared from an ethylene/aminoalkyl acrylatecompound copolymer.

Secondly, the aqueous dispersion according to this invention ischaracterized by markedly improved effects to simultaneously impartsizing properties and wet strength over the aforesaid conventionalaqueous dispersions, so that a desired level of performance on practicaluse can be achieved with a reduced amount of the additive.

DETAILED DESCRIPTION OF THE INVENTION

The ethylene copolymer which can be used as a starting material can beprepared by radical polymerization of from 40 to 80% by weight,preferably from 50 to 75% by weight, of ethylene and from 20 to 60% byweight, preferably from 25 to 50% by weight, of at least one aminoalkylacrylamide comonomer represented by formula (I) under high temperatureand high pressure conditions.

If the content of the aminoalkyl acrylamide comonomer unit in theethylene copolymer is less than 20% by weight, i.e., if the ethyleneunit content is more than 80% by weight, the product resulting from theaddition reaction between the quaternary salt and an epihalohydrincompound would have poor hydrophilicity, failing to provide a stableaqueous dispersion comprising uniform fine particles. On the other hand,if the ethylene unit content is less than 40% by weight, i.e., theaminoalkyl acrylamide comonomer unit content exceeds 60% by weight, theresulting aqueous dispersion only forms a coating film havinginsufficient water resistance and too low film strength. When such afilm is used as a conductive layer of an electrographic recordingmaterial, writing with a pencil or a ball-point pen would be impossible,or when such an aqueous dispersion is used as an additive for paper, theimproving effects on sizing properties would be insufficient.

From the standpoint of viscosity of the aqueous dispersion and physicalproperties of a coating film formed by the aqueous dispersion, andparticularly film strength, the ethylene copolymer to be used in thepresent invention should have a melt index of from 10 to 1,000 g/10 min,preferably from 30 to 500 g/10 min, as measured according to JIS K-6760.

The above-described ethylene copolymer can be prepared by high-pressureradical polymerization in accordance with the process described, e.g.,Japanese Patent Publication Nos. 22523/67 and 5194/78. Morespecifically, ethylene and the aminoalkyl acrylamide compound of formula(I) are continuously fed to a vessel-type reactor with a stirrer or atubular-type reactor together with a free-radical catalyst, such asoxygen, organic peroxides, diazo compounds, etc., to effectpolymerization at a pressure of from 500 to 3,000 kg/cm.sup. and at atemperature of from 100° to 300° C. Various chain transfer agents, suchas ethane, propane, propylene, etc., may be used to regulate themolecular weight of the polymer

Specific examples of the aminoalkyl acrylamide comonomers which can beused preferably in the present invention are dimethylaminoethylacrylamide, dimethylaminopropyl acrylamide, dimethylaminobutylacrylamide, diethylaminoethyl acrylamide, diethylaminopropyl acrylamide,diethylaminobutyl acrylamide, di-n-propylaminoethyl acrylamide,di-n-propylaminopropyl acrylamide,N-(1,1-dimethyl-3-dimethylaminopropyl) acrylamide, etc., andmethacrylamide derivatives corresponding to these acrylamidederivatives. These aminoalkyl acrylamide comonomers may be used eitherindividually or in combinations of two or more thereof.

Among the above-enumerated comonomers, more preferred aredimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide,dimethylaminoethyl acrylamide, and dimethylaminoethyl methacrylamide.

For the purpose of enhancing softness of a coating film formed by theaqueous dispersion or lowering a heat-sealing temperature, the ethylenecopolymer may further comprise one or more comonomers other thanethylene and the aminoalkyl acrylamide compound, such as methylacrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, vinylacetate, vinyl propionate, dimethylaminoethyl methacrylate,dimethylaminoethyl acrylate, and the like, at a ratio up to 20% byweight.

The amount of hydrochloric acid to be used in quaternarization of theethylene copolymer ranges from 50 to 200 parts, preferably from 80 to150 parts, by mole per 100 parts by mole of the amino group in theethylene copolymer. If the amount of hydrochloric acid is less than 50parts, the resulting quaternary salt would have poor hydrophilicity, andthe addition product obtained by the subsequent reaction with anepihalohydrin compound cannot provide a stable and low-viscosity aqueousdispersion comprising uniform fine particles. On the other hand, if theamount of hydrochloric acid exceeds 200 parts, a coating film formed bythe resulting aqueous dispersion would have insufficient waterresistance and film strength.

The quaternarization of the ethylene copolymer with hydrochloric acidcan sufficiently be achieved by adding usually from 5 to 35 parts byweight of the ethylene copolymer in the form of pellets or powders andhydrochloric acid to 100 parts by weight of water and stirring themixture at a temperature of from 60° to 100° C. for a period of from 30to 120 minutes under atmospheric pressure. In some cases, the ethylenecopolymer retains its shape during the quaternarization reaction whilemerely being swollen with a hydrochloric acid aqueous solution. Such astate gives rise to no problem since the reaction system turns to be anaqueous dispersion comprising fine particles through the subsequentaddition reaction with an epihalohydrin compound.

The thus prepared quaternary hydrochloride of the ethylene copolymer isthen addition reacted with an epihalohydrin compound to thereby form auniform and stable aqueous dispersion.

The epihaloydrin compound to be reacted includes epichlorohydrin,epibromohydrin, etc., with epichlorohydrin being particularly preferred.The epihalohydrin-compound is used in an amount of from 50 to 200 partsby mole, preferably from 80 to 150 parts by mole, per 100 parts by moleof the amino group contained in the ethylene copolymer. When the amountof the epihalohydrin compound is less than 50 parts, a stable andlow-viscosity aqueous dispersion comprising uniform fine particlescannot be obtained. If it exceeds 200 parts, the resulting aqueousdispersion only forms a coating film having insufficient waterresistance and small film strength, causing problems on practical use.

The addition reaction with the epihalohydrin compound can be usuallycarried out under stirring at a temperature ranging from 20° to 100° C.,preferably from 40° to 90° C., for 30 to 300 minutes. The mode offeeding the epihalohydrin compound is not particularly limited, and itcan be fed all at once, continuously, or intermittently.

If desired, the thus prepared cationic polymer aqueous dispersionaccording to the present invention may be subjected to heat treatment inthe presence of an alkylolamine compound. The aqueous dispersionobtained by this heat treatment provides a coating film having a furtherreduced surface resistivity.

The alkylolamine compound to be used includes ethanolamine,diethanolamine, triethanolamine, isopropanolamine, diisopropanolamine,triisopropanolamine, dihydroxypropylamine, bis(dihydroxypropyl)amine,tris(dihydroxypropyl)amine, and the like. In addition,polyamine-polyhydric alcohol compounds obtained by reacting a polyamineand an alkylene oxide, such as an ethylene oxide (4 mols) adduct ofethylenediamine, an ethylene oxide (4 mols) adduct of propylenediamine,etc., may also be employed Of these alkylolamine compounds preferred isdiethanolamine.

The alkylolamine compound is added in a amount of from 20 to 200 partsby mole, preferably from 50 to 150 parts by mole, per 100 parts by moleof the amino group present in the ethylene copolymer. Amounts less than20 parts are not enough to produce desired effects to reduce a surfaceresistivity of a coating film formed by the resulting aqueousdispersion. On the other hand, if the amount of the alkylolaminecompound exceeds 200 parts, since the excess remains unreacted in theresulting aqueous dispersion, a coating film obtained therefrom becomesnot only non-uniform but hygroscopic, resulting in increased humiditydependence of surface resistivity.

The reaction with the alkylolamine compound is usually carried out at atemperature of from 20° to 100° C., preferably from 40° to 100° C., fora period of from 1 to 10 hours.

The cationic polymer aqueous dispersion according to the presentinvention preferably has a solids content ranging from 5 to 50 parts,more preferably from 10 to 40 parts, by weight per 100 parts by weightof water content. The term "solids content" as used herein means anonvolatile content which is left after removing water from the aqueousdispersion by drying in hot air at about 100° C. An aqueous dispersionhaving a solids content exceeding 50 parts has no fluidity due to toohigh a viscosity and is inferior in processability, such as coatingproperties on a substrate. An aqueous dispersion having a solids contentless than 5 parts is unfavorable for production efficiency and also fromthe standpoint of distribution cost and drying load after coating.

In the film formation, the aqueous dispersion is coated on a substrate,e.g., paper and a plastic film, and dried by heating at about 50° C. to150° C.

In the cases where the aqueous dispersion of the invention is used as aconductive layer of an electrographic recording material, it may bemixed with a metal oxide semi-conductor, e.g., zinc oxide, cuprousoxide, indium oxide, tin oxide, titanium oxide, cobalt oxide, nickeloxide, tantalum pentoxide, vanadium pentoxide, tungsten trioxide,molybdenum trioxide, etc., or these metal oxides doped with a dopant.The combined use of these metal oxide semi-conductors is effective tofurther decrease surface resistivity of the resulting conductive layerand also to reduce humidity dependence of recording density.

As a resin solution for a dielectric layer which is to be applied ontothe semi-conductive laminate prepared by coating the aqueous dispersionof the invention on a paper or plastic film and then drying, in order toimparting writing properties, marking properties, or natural feeling toacrylic resins, vinyl chloride resins, butyral resins, etc., paintshaving dispersed therein pigments (e.g., titanium oxide, calciumcarbonate, starch, clay, etc.) in the finely granular state aregenerally used. These paints are applied in a thickness of from about 5to 10 μm on a dry basis. The surface resistivity thereof is preferablyfrom about 10¹² to 10¹⁵ Ω at ordinary temperature and at atmosphericpressure.

If desired, it is also possible to incorporate into the aqueousdispersion of the invention additives, such as dyes, pigments, fillers,surface .active agents, antistatics, plasticizers, lubricants,dispersing agents, defoaming agent, etc., and water-soluble resins,e.g., polyvinyl alcohol.

According to the present invention, a thin, transparent, soft, and toughcoating film can be obtained by coating the aqueous dispersion on apaper or plastic film substrate, followed by drying. The coating filmafter drying becomes water-insoluble to exhibit excellent stabilityagainst humidity or water. Therefore, an electrographic recordingmaterial in which the conductive layer comprises the aqueous dispersionof the present invention has small dependence of recording density onhumidity and is free from changes in recording performance with a lapseof time. When the aqueous dispersion is used as an antistatic, theresulting film exhibits long-lasting antistatic properties.

Further, use of the aqueous dispersion of the present invention as anadditive in the sheet forming process results in marked improvements onboth sizing properties and wet strength of paper. In this application,the aqueous dispersion may be either added to a pulp slurry as a wet endadditive or impregnated into paper. In the former case, the cationicpolymer as dispersed in water is usually added to a pulp slurry in anamount of from 0.1 to 5 parts by weight per. 100 parts by weight of pulpon dry basis, and the formed sheet is then dried by heating at atemperature of from 70° to 150° C. for a period of from several secondsto several minutes. In this case, a water repellent, such as waxes,silicones, and fluorohydrocarbon resins, and the like, may be used incombination.

The present invention will now be illustrated in greater detail withreference to the following examples, but it should be understood thatthe present invention is not deemed to be limited thereto. In theseexamples, all the percents and ratios are given by weight unlessotherwise indicated.

EXAMPLE 1

In a 1,000 ml-volume glass-made flask were charged 360 g of water, 100 gof pellets of an ethylene/dimethylaminopropyl acrylamide copolymerhaving an ethylene/dimethylaminopropyl acrylamide ratio of 59:41 and amelt index of 300 g/10 min (as measured according to JIS K-6760,hereinafter the same), and 27 g of a 36% hydrochloric acid aqueoussolution. The amount of the hydrochloric acid charged corresponded to100 parts by mole per 100 parts by mole of the amino group in thecopolymer. The temperature of the mixture was elevated from roomtemperature to 100° C. over a period of 30 minutes while stirring, atwhich point the stirring was continued for an additional 60 minutesunder refluxing whereby the pellets were destroyed to obtain a viscousaqueous slurry.

After cooling to 80° C. while stirring, 24 g (corresponding to 100 partsby mole per 100 parts by mole of the amino group in the copolymer) ofepichlorohydrin was added dropwise to the slurry over a period of 30minutes. The stirring was further continued for 270 minutes at 80° C. toprepare a pale brown uniform aqueous dispersion. The resulting aqueousdispersion was designated as Dispersion A-1. Dispersion A-1 had a pH of5.6 at 25° C. and a viscosity of 49 cps at 25° C. The dispersed polymerparticles had a particle size of 0.1 μm or less. Dispersion A-1 had asolids content (hereinabove defined) of 26%.

EXAMPLE 2

In a 1,000 ml-volume glass-made flask was put 490 g of Dispersion A-1prepared in Example 1, and 28 g (corresponding to 100 parts by mole per100 parts by mole of the amino group in the copolymer) of diethanolaminewas added thereto while stirring at 80° C. The stirring was continued atthat temperature for an additional 300 minutes, followed by cooling toobtain a pale brown uniform aqueous dispersion. The resulting dispersionwas designated as Dispersion A-2. Dispersion A-2 had a pH of 6.9 at 25°C., a viscosity of 17 cps at 25° C., and a solids content of 30%. Thedispersed polymer particles had a particle size of 0.1 μm or less.

EXAMPLES 3 TO 8

Dispersions A-3 to A-8 were prepared in the same manner as in Example 1or 2, except for replacing the ethylene/dimethylaminopropyl acrylamidecopolymer as used in Example 1 or 2 with pellets of various ethylenecopolymers whose compositions and melt indices are shown in Table 1.Each of Dispersions A-3 to A-8 was a stable and low-viscosity aqueousdispersion comprising polymer particles having a particle size of 1 μmor less.

REFERENCE EXAMPLES 1 TO 3

In order to evaluate performance of the aqueous dispersions according tothe present invention as a conductive coating or an additive in papermanufacturing, comparative aqueous Dispersions R-1 to R-3 were preparedin the same manner as in Example 1 or 2, except for replacing theethylene/dimethylaminopropyl acrylamide copolymer with copolymerscomprising ethylene and an aminoalkyl acrylate comonomer as shown inTable 1. Any of Dispersions R-1 to R-3 had dispersion properties similarto the aqueous dispersions obtained in Examples 1 and 2, i.e., lowviscosity and a particle size of 1 μm or less.

REFERENCE EXAMPLE 4

The same ethylene copolymer as used in Example 5 (dimethylaminopropylacrylamide content: 50%) was quaternarized using 1.3 molar times ofhydrochloric acid in the same manner as in Example 1 to prepare aquaternary salt having a solids content of 24%. The product was aviscous solid-liquid mixture in the form of a slurry. Making acomparison with Example 5, it is apparent that subsequent addition ofepichlorohydrin is essential for obtaining a stable aqueous dispersioncomprising fine particles.

REFERENCE EXAMPLES 5 AND 6

The procedure of Example 1 or 2 was followed, except for starting withan ethylene copolymer having a dimethylaminopropyl acrylamide content of15% and a melt index of 100 g/10 min, but the attempt to form a uniformaqueous dispersion failed because the pellets of the copolymer were notcompletely destroyed.

                                      TABLE 1                                     __________________________________________________________________________                     Amount of                                                                            Amount of                                             Ethylene Copolymer                                                                             Hydrochloric                                                                         Epichloro-                                                                           Alkylolamine                                                Melt                                                                              Acid   hydrin     Amount Aqueous Dispersion                  Comonomer    Index                                                                             (molar ratio                                                                         (molar ratio                                                                             (molar ratio                                                                         Solids Viscosity                    (Content:    (g/10                                                                             to amino                                                                             to amino   to amino                                                                             Content                                                                              (25° C.)                                                                    Uniform-                                                                           Sample             wt %)        min)                                                                              group) group) Kind                                                                              group) (wt %)                                                                             pH                                                                              (cps)                                                                              ity  No.                __________________________________________________________________________    Example                                                                       No.                                                                           1     PAA.sup.1                                                                         (41)                                                                             300 1.0    1.0    --  --     26   5.6                                                                             49   good A-1                2     "   "  "   "      "      DEA.sup.5                                                                         1.0    30   6.9                                                                             17   good A-2                3     "   "  "   "      "      MEA.sup.6                                                                         "      25   7.1                                                                             32   good A-3                4     "   (35)                                                                             280 "      "      DEA 2.0    25   7.3                                                                             20   good A-4                5     "   (50)                                                                              55 1.3    1.5    --  --     27   6.7                                                                             35   good A-5                6     PMA.sup.2                                                                         (39)                                                                             270 1.0    1.0    --  --     22   6.5                                                                             31   good A-6                7     "   "  "   "      "      DEA 2.0    25   6.8                                                                             20   good A-7                8     "   (28)                                                                              96 1.2    1.2    --  --     17   6.7                                                                             84   good A-8                Reference                                                                     Example                                                                       1     EM.sup.3                                                                          (39)                                                                             300 1.0    1.0    --  --     25   5.5                                                                             42   good R-1                2     "   "  "   "      "      DEA 1.0    30   7.1                                                                              9   good R-2                3     EA.sup.4                                                                          (35)                                                                             250 "      "      "   2.0    25   7.3                                                                             52   good R-3                4     PAA.sup.1                                                                         (50)                                                                              55 1.3    0      --  --     24   4.4                                                                             870  poor --                 5     "   (15)                                                                             100 1.0    1.0    --  --     20   6.6                                                                             --   poor --                 6     "   "  "   "      "      DEA 1.0    22   7.0                                                                             --   poor --                 __________________________________________________________________________     Note:                                                                         .sup.1 Dimethylaminopropyl acrylamide                                         .sup.2 Dimethylaminopropyl methacrylamide                                     .sup.3 Dimethylaminoethyl methacrylate                                        .sup.4 Dimethylaminoethyl acrylate                                            .sup.5 Diethanolamine                                                         .sup.6 Monoethanolamine                                                  

EXAMPLE 9

Dispersion A-2 prepared in Example 2 was coated on wood free paperhaving a basis weight of 84 g/m² by means of a bar coater #10 and driedat 100° C. for 5 minutes in a hot air-circulating drier to obtaincurling-free coated paper having formed thereon a uniformsemi-conductive film having a dry weight of 1.2 g/m².

Surface resistivity of the coated surface of the paper was determined bythe use of a resistance meter (Super-insulation meter SM-10E model,manufactured by Toa Denpa Kogyo K. K.) under conditions of 23° C. intemperature, 30%, 50%, or 70% in relative humidity (RH), and 100 V inapplied voltage and was found to be 5×10⁷ Ω, 8×10⁶ Ω, 9×10⁵ Ω,respectively, as shown in Table 2. The surface resistivity of paperbefore coating was 4×10¹³ Ω at 50% RH.

A coating agent for a dielectric layer "C" (methyl ethyl ketone solutionof a vinyl acetate/vinyl chloride/vinyl alcohol terpolymer resinproduced by Sakata Shokai K. K.; solids content: 28%) and "Softon.sup.®1800" (a registered trade name of calcium carbonate fine powdersproduced by Bihoku Funka Kogyo K. K.; mean particle size: 1.25 μm) weremixed at a weight ratio of 70:30 to prepare a dispersion. The resultingdispersion was coated on the semi-conductive film of the above-obtainedcoated paper by the use of a bar coater #10, air-dried in a draft, anddried in a circulating hot-air drier at 100° C. for 5 minutes to obtainelectrographic recording paper having a coating layer of 6.0 g/m² intotal dry weight.

When an electrographic recording test was carried on the resultingelectrographic recording paper at 30% RH by the use of an electrographicrecording testing machine (Electrographic Plotter EP101, AO type;manufactured by Matsushita Denso K. K.), a very sharp recorded patterncould be obtained.

EXAMPLES 10 TO 13

Curling-free coated paper having a uniform and glossy coating film wasprepared in the same manner as in Example 9, except for replacingDispersion A-2 with Dispersions A-3, A-4, A-5, or A-7 obtained inExamples 3, 4, 5, or 7, respectively. Each of the resulting coatedpapers had a satisfactory level of surface resistivity as indicated inTable 2.

The coated paper was further coated with a dielectric layer in the samemanner as in Example 9 to obtain electrographic recording paper. Theresulting recording paper exhibited excellent recording performance ineach case.

COMPARATIVE EXAMPLES 1 AND 2

Coated paper was prepared in the same manner as in Example 9, except forreplacing Dispersion A-2 with Dispersion R-2 or R-3 prepared inReference Example 2 or 3, respectively. Surface resistivities of theresulting coated papers were relatively high as shown in Table 2.Therefore, electrographic recording paper produced from each of thesecoated papers in the same manner as in Example 9 showed poor recordingperformance only providing totally unclear patterns from which many dotsvanished.

From the foregoing, it can be seen that the aqueous dispersions preparedfrom the ethylene/aminoalkyl acrylamide compound copolymer according tothe present invention forms a coating film having higher electricalconductivity, which leads to production of electrographic recordingpaper exhibiting higher performance, than the aqueous dispersionsprepared from the ethylene/aminoalkyl acrylate copolymer.

                                      TABLE 2                                     __________________________________________________________________________           Aqueous Dispersion           Electrographic                                         Coating Weight                                                                        Coated Paper   Recording                                 Example      (on dry basis)                                                                        Surface Resistivity (Ω)                                                                Performance                               No.    Sample No.                                                                          (g/m.sup.2)                                                                           30% RH                                                                             50% RH                                                                             70% RH                                                                             (30% RH, 23° C.)                   __________________________________________________________________________    Example 9                                                                            A-2   1.2     5 × 10.sup.7                                                                 8 × 10.sup.6                                                                 9 × 10.sup.5                                                                 good                                      Example 10                                                                           A-3   1.0     7 × 10.sup.7                                                                 1 × 10.sup.7                                                                 2 × 10.sup.6                                                                 good                                      Example 11                                                                           A-4   1.2     7 × 10.sup.7                                                                 9 × 10.sup.6                                                                 9 × 10.sup.5                                                                 good                                      Example 12                                                                           A-5   1.7     8 × 10.sup.7                                                                 7 × 10.sup.6                                                                 8 × 10.sup.5                                                                 good                                      Example 13                                                                           A-7   1.3     6 × 10.sup.7                                                                 9 × 10.sup.6                                                                 1 × 10.sup.6                                                                 good                                      Comparative                                                                          R-2   1.2     4 × 10.sup.8                                                                 5 × 10.sup.7                                                                 6 × 10.sup.6                                                                 poor                                      Example 1                                                                     Comparative                                                                          R-3   1.0     5 × 10.sup.8                                                                 6 × 10.sup.7                                                                 7 × 10.sup.6                                                                 poor                                      Example 2                                                                     __________________________________________________________________________

EXAMPLE 14

To 100 g of Dispersion A-1 prepared in Example 1 was added 25 g ofpowderous conductive zinc oxide (produced by Honjo Chemical K. K.; meanparticle size: 1.5 μm; disclosed in Japanese Patents 1,029,615 and1,029,616), and the mixture was stirred at room temperature for 30minutes to prepare a gray mixture having uniformly dispersed thereinzinc oxide particles. The resulting mixture was coated on wood freepaper having a basis weight of 84 g/m² with a bar coater #10 and driedin hot air of 110° C. for 3 minutes to obtain coated paper havingprovided thereon a uniform white coating film having a dry weight of 7.6g/m². The surface resistivities of the coated paper were measured underthe same conditions as in Example 9 and found to be 2×10⁶, 7×10⁵, and5×10⁵ Ω at 30, 50, and 70% RH, respectively, indicating that the coatedpaper had low resistivity with small dependence on humidity.

Separately, a uniform dispersion was prepared by mixing 100 g of acoating agent for a dielectric layer "50C" (a toluene solution of anacrylic resin produced by Nagase Kasei Kogyo K. K.; solids content:50%), 50 g of the same calcium carbonate as used in Example 9, and 180 gof toluene with stirring. The dispersion was coated on the aboveprepared coated paper with a bar coater #10 and dried in hot air at 110°C. for 5 minute to obtain electrographic recording paper having a totalcoating dry weight of 13.1 g/m².

When an electrographic recording test was carried out under the sameconditions as in Example 9, a very clear recorded pattern free fromdisappearance of dots was obtained.

EXAMPLE 15

To 100 g of Dispersion A-5 prepared in Example 5 was added 18 g offlaky, transparent, and conductive mica "MEC-500" (mica particles havinga mean particle size of 10 μm and a specific surface area of 19 m² /gcoated with tin oxide and antimony oxide; produced by Teikoku Kako K.K.), followed by stirring at room temperature for 30 minutes to preparea gray mixture having uniformly dispersed therein the mica particles.The mixture was coated on a corona-treated surface of a 75 μm thickpolyethylene terephthalate film "E-5101" (produced by Toyobo Co., Ltd.)by the use of a bar coater #10 and dried in hot air at 120° C. for 2minutes to obtain a laminated film having a glossy, transparent, andhighly adhesive coating film having a dry weight of 8.5 g/m². Thesurface resistivities of the coating film were found to be 9×10⁵, 5×10⁵,and 3×10.sup. 5 Ω at 30, 50, and 70% RH, respectively, as measured underthe same conditions as in Example 9, indicating that the laminated filmhad low resistivity with small dependence on humidity.

A dielectric layer was formed on the laminated film in the same manneras in Example 14 to obtain semi-transparent laminated film forelectrographic recording having provided thereon coating layers having atotal dry weight of 14.7 g/m² and a haze of 76%. As a result of anelectrographic recording test under the same conditions as in Example 9,a very clear pattern free from dot disappearance was obtained.

EXAMPLES 16 TO 18

To a 1.0% pulp slurry having a Canadian Standard drainage rate of 410 ccand an N-BKP/L-BKP ratio of 1/1 was added Dispersions A-1, A-5 or A-7 inan amount indicated in Table 3, and the mixture was stirred at 200 rpmfor 2 minutes. The slurry was formed into sheet by means of a TAPPIstandard sheet machine and dried at 110° C. for a prescribed period (1minute or 10 minutes) to obtain paper having a basis weight of 80 g/m².The degree of sizing and wet breaking length as a measure of wetstrength of the resulting paper were determined as follows, and theresults obtained are shown in Table 3.

(1) Degree of Sizing

Determined in according to a Stockigt method at 25° C. and 65% RH.

(2) Wet Breaking Length (measured according to JIS P8113)

Wet tensile strength after immersion in water at 20° C. for 60 minuteswas measured, and a wet breaking length was calculated therefromaccording to equation: ##EQU1##

COMPARATIVE EXAMPLES 3 AND 4

Paper samples were prepared in the same manner as in Examples 16 to 18,except for replacing the aqueous dispersion of the invention withDispersion R-1 or R-2 prepared in Reference Example 1 or 2. The degreeof sizing and wet breaking length of the resulting paper were determinedin the same manner as in Examples 16 to 18, and the results obtained areshown in Table 3.

Making comparisons with the results of Examples 16 to 18, it is apparentthat the aqueous dispersions according to the present invention producegreater effects to improve both degree of sizing and wet strength thanthose obtained by the aqueous dispersions prepared from anethylene/aminoalkyl acrylate compound copolymer.

COMPARATIVE EXAMPLE 5

Paper samples were prepared in the same manner as in Examples 16 to 18,except for replacing the aqueous dispersion of the present inventionwith "Sumirez Resin.sup.® #675" (polyamide-epichlorohydrin type wetstrength resin produced by Sumitomo Chemical Co., Ltd.; 25% aqueoussolution). The degree of sizing and wet breaking length were determinedin the same manner as in Examples 16 to 18, and the results obtained areshown in Table 3. It is revealed from Table 3 that the addition of thewet strength resin produces no sizing effect at all.

                                      TABLE 3                                     __________________________________________________________________________                           Drying Time: 1 min                                                                           Drying time: 10 min                            Aqueous Dispersion                                                                            Degree of                                                                           Wet      Degree of                                                                           Wet                                              Amount added                                                                          Sizing                                                                              Breaking Length                                                                        Sizing                                                                              Breaking Length                   Example No.                                                                          Sample No.                                                                            (wt %)  (sec) (km)     (sec) (km)                              __________________________________________________________________________    Example 16                                                                           A-1     0.4     59    1.80     65    1.86                                             0.8     88    2.57     90    2.62                                             2.0     97    3.82     99    3.86                              Example 17                                                                           A-5     0.4     54    1.74     56    1.82                                             0.8     86    2.64     97    2.65                                             2.0     100   3.91     104   3.97                              Example 18                                                                           A-7     0.4     51    1.76     53    1.79                                             0.8     82    2.46     89    2.51                                             2.0     101   3.72     104   3.94                              Comparative                                                                          R-1     0.4     43    1.45     49    1.51                              Example 3      0.8     72    2.20     81    2.23                                             2.0     90    3.26     92    3.39                              Comparative                                                                          R-2     0.4     40    1.52     43    1.55                              Example 4      0.8     69    2.33     75    2.37                                             2.0     88    3.48     90    3.51                              Comparative                                                                          Sumirez 0.4      0    0.78      0    1.32                              Example 5                                                                            Resin ® #675                                                                      0.8      0    1.08      0    1.92                                             2.0      0    0.24      0    2.70                              Control                                                                              none    --       0    0.24      0    0.25                              Example                                                                       __________________________________________________________________________     Note:                                                                         *Based on the weight of the pulp.                                        

EXAMPLES 19 AND 20

Hand-made unsized paper (10 cm x 30 cm) having a basis weight of 80 g/m²was dipped in 500 ml of Dispersion A-5 or A-8 diluted so as to have apolymer concentration as shown in Table 4 below and then dried in hotair of 110° C. for 5 minutes. The pickup of the polymer based on theweight of the unsized paper is shown in Table 4. The degree of sizingand wet breaking length of the resulting impregnated paper weredetermined in the same manner as in Examples 16 to 18, and the resultsobtained are shown in Table 4. Table 4 demonstrates the effects exertedon both degree of sizing and wet strength.

                  TABLE 4                                                         ______________________________________                                                                          Degree                                                                              Wet                                                  Polymer     Polymer                                                                              of    Braking                               Example                                                                              Sample  Concentration                                                                             Pickup Sizing                                                                              Length                                No.    No.     (wt %)      (wt %) (sec) (km)                                  ______________________________________                                        19     A-5     0.1         0.1    41    0.79                                                 1.0         1.1    92    2.58                                                 2.0         2.4    102   3.73                                  20     A-8     0.1         0.1    45    0.71                                                 1.0         1.2    97    2.42                                                 2.0         2.7    105   3.57                                  Control                                                                              none    --          --      0    0.24                                  Example                                                                       ______________________________________                                    

As described above, the aqueous dispersion prepared from a copolymer ofethylene and an aminoalkyl acrylamide comonomer according to the presentinvention, when coated and dried on a substrate, provides a coating filmhaving a significantly improved level of electrical conductivity and is,therefore, sufficiently applicable, for instance, as a polymer for aconductive layer of electrographic recording material.

Further, the aqueous dispersion of the present invention also serves asa wet end additive or an impregnant for paper to simultaneously improvedegree of sizing and wet strength.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A method for producing an aqueous dispersion of acationic polymer comprising the steps of:(1) reacting an ethylenecopolymer comprising from 40 to 80% by weight of ethylene and from 20 to60% by weight of at least one aminoalkyl acrylamide comonomerrepresented by formula (I): ##STR3## wherein R₁ represents a hydrogenatom or a methyl group; R₂ and R₃ each represents a hydrogen atom or analkyl group having from 1 to 4 carbon atoms; and n represents an integerfrom 2 to 4, where said comonomer has a melt index, as measured inaccordance with JIS K-6760, of from 10 to 1,000 g/10 min withhydrochloric acid in water to form a quaternary salt; and (2) reactingsaid quaternary salt of step (1) with an epihalohydrin compound in anamount of from 50 to 200 parts by mole per 100 parts by mole of theamino group contained in said ethylene copolymer.
 2. A method forproducing an aqueous dispersion of a cationic polymer as claimed inclaim 1, wherein said aminoalkyl acrylamide comonomer or comonomersis/are selected form dimethylaminopropyl acrylamide, dimethylaminopropylmethacrylamide, dimethylaminoethyl acrylamide, and dimethylaminoethylmethacrylamide.
 3. A method for producing an aqueous dispersion of acationic polymer as claimed in claim 1, wherein said epihalohydrincompound is epichlorohydrin.